The present invention relates generally to a process for forming a flange on a hollow body of thermoplastic material, and apparatus for carrying out such a process.
The above-mentioned hollow body which is to be provided with a flange configuration may be for example a hollow molded article or blank which comprises a substantially cylindrical wall portion defining an opening at one end and having a bottom at the other end, thus providing a can-like shape. The flange to be provided on the can shape constitutes for example a beaded mounting edge for mounting a cover or lid member thereon. The blank which is to be provided with the flange may be produced by means of various processes, one of which provides that a preform which is produced for example by injection molding and which comprises a substantially cylindrical wall portion, a bottom portion at one end and an opening at the other end, is converted into an intermediate product by stretching of the cylindrical wall portion at a temperature below the vitreous transition temperature of the material forming the preform, the intermediate product then being subjected to a preliminary expansion operation at its open end and then, starting from that open end in pre-expanded condition, expanded at least over the major part of its longitudinal extent and then subjected to thermofixing to establish the configuration of the blank. The above-mentioned flange or beaded edge portion is then formed on the thermofixed blank. It is also possible however for a can-like hollow body of that nature to be produced by means of a stretching blowing process which involves using a blowing mold to produce an initially substantially closed hollow body whereupon, to produce the opening in the hollow body, the end region of the blank which is remote from the end portion thereof is cut off. Both those forms of process result in an article in which at least the material forming the wall portion is oriented in order thereby to improve its mechanical characteristics and properties.
Irrespective of the method of manufacture of the hollow body on which a flange is to be formed and irrespective also of the use to which such a hollow body is subsequently to be put, in most cases the final article is a mass-produced article which is to be manufactured in large numbers so that the operating procedure involved in the process, and also the equipment used for carrying the process into effect, should be as simple and as straightforward as possible, so that it is accordingly reliable.